The 5,000-year-old ceremonial site is thought to have been a key stop along an ancient route between a land of the living, several miles away, and a domain of the dead—Stonehenge. At least one archaeologist thinks Bluestonehenge may have been a sort of crematorium.

Named for the color of its long-gone stones, Bluestonehenge, or Bluehenge, was dismantled thousands of years ago, and many of its standing stones were integrated into Stonehenge during a rebuilding of the larger monument, according to the archaeologists.

Mini-Stonehenge: Prehistoric Crematorium?

Bluestonehenge was found in August along the banks of the River Avon during excavations led by Mike Parker Pearson of the University of Sheffield in the U.K.

The circle of an estimated 25 bluestones was surrounded by a henge—an earthwork with a ditch and bank. The henge has been tentatively dated to 2400 B.C. But flint arrowheads found at the stone-circle site are of a type that suggests the rocks were erected as early as 3000 B.C.

More precise dates will have to wait until prehistoric deer antlers—used as pickaxes at Bluestonehenge—have been radiocarbon dated, the team said.

Made from a hard dolerite rock, the four-ton megaliths were hewn from ancient quarries in the Preseli Mountains of Wales, 150 miles (240 kilometers) away, Parker Pearson said. The manpower and logistics required to transport the stones suggests they had deep significance to ancient Britons, experts say.

Unlike Stonehenge, which aligns with the sun at the summer and winter solstices, Bluestonehenge shows no sign of a particular orientation, or even an entrance, the team reported.

However Bluestonehenge's empty stone holes were filled with charcoal, indicating that large amounts of wood were burned there—signifying, perhaps, a prehistoric crematorium. Perhaps not coincidentally, ashes have been found in holes at Stonehenge.

"Maybe the bluestone circle is where people were cremated before their ashes were buried at Stonehenge itself," Parker Pearson said in a statement.

Parker Pearson proposes that Stonehenge represented a "domain of the dead" to ancestor-worshiping ancient Britons.

The Bluestonehenge discovery was made as part of the Stonehenge Riverside Project, a seven-year archaeological investigation of the Stonehenge area, supported in part by the National Geographic Society's Committee for Research and Exploration. (The National Geographic Society owns National Geographic News.) Other funders include the U.K. Arts and Humanities Research Council.

Key Piece in Stonehenge Puzzle

Bluestonehenge may represents a vital part of the jigsaw as researchers slowly piece together the meaning of Stonehenge.

"Maybe we need to actually start thinking about Stonehenge as a series of stone structures that are not necessarily all contained within that circular ditch [at Stonehenge proper]," added Pitts, who was not involved in the project.

The excavation team now believes Stonehenge incorporates the 25 bluestones that originally stood at Bluestonehenge. Only a few bluestone pieces were found at the new site, and "that is telling you that the stones are being taken out whole," said dig co-director Julian Thomas of the University of Manchester.

Bluestonehenge's stones were dragged along the avenue to Stonehenge during a major rebuilding phase around 2500 B.C., the archaeologists speculated (time line of the stages of Stonehenge).

If Bluestonehenge had been demolished much later—in Roman times, when reverence for the stones would have been diminished, for example—"they'd be breaking them up and turning them into building stone," Thomas said.

"I think it's very likely that the new stone circle is contemporary with the very earliest stages of Stonehenge," the archaeologist added.

British Archaeology's Pitts agreed that Bluestonehenge's rocks were likely appropriated for Stonehenge.

"It makes a lot of sense," Pitts said. "The megaliths that were in the pits down by the river had to have gone somewhere, and they clearly weren't broken up at the site, because its not covered [in fragments] of stone."

Previous excavations have drawn a picture of seasonal festivities at Durrington Walls, which some see as part of the "domain of the living" in the spiritual geography of the people of Stonehenge.

The dead would be celebrated at Durrington, then carried along a short avenue to the River Avon, archaeologists speculate. The procession would continue down the river, then "dock" at the foot of the avenue leading to Stonehenge—stopping, it's now thought, at Bluestonehenge, perhaps for cremation, before continuing to Stonehenge for burial.

"We tend to think of monuments as cultural, and a river or a mountain as something that's natural," he added. "What's fascinating about the Stonehenge complex is that these different elements are being threaded together.

"By constructing these monuments you're not just adding a cultural veneer on the surface, you're actually reengineering the world."

Given the Bluestonehenge discovery, British Archaeology's Pitts said, "I'm sure there are very significant discoveries still to be made in this landscape."